Parathyroid venous sampling remains the most precise localization technique for patients with failed parathyroid surgery but it requires considerable experience on the part of the angiographer as well as prolonged catheter manipulation to sample the multiple small veins draining the neck and mediastinum. Knowledge of the presence of parathyroid hormone (PTH) gradients during the procedure would enable the angiographer to focus on a specific area, perhaps obtaining more detailed samples and to shorten the procedure when significant gradients occur in the early samples. This protocol will not increase the accuracy of sampling but will shorten the procedure, reduce radiation exposure to the patient and to the interventional radiologist and allow more precise localization by more focused sampling. The success of another protocol 94-DK-0195 has decreased the number of patients who need parathyroid venous sampling so our original estimates of the frequency of the study are no longer valid. At the current time, it would be difficult to accrue enough patients to complete this study in a timely fashion. The test has proven effective in the few OR patients accrued and we no longer consider it to be investigational. It is now used in routine patient care when needed. No new subjects were enrolled this year. We have terminated this protocol.